1. Field of the Invention
The present invention relates to a liquid crystal display device and, in particular, to a liquid crystal display device suitable for use in a reflection type liquid crystal display device such as an STN type color liquid crystal display device utilizing the STN (super-twisted nematic) effect.
2. Description of the Related Art
A liquid crystal display device contains a liquid crystal module in which a liquid crystal layer is formed between transparent substrates such as two glass substrates. One of the conventional types of liquid crystal display devices is a light reception type (non-light-emission type) flat (flat panel) display device utilizing changes in the optical natures of a medium. This liquid crystal display device is of a transmission type in which a backlight is provided on the back side, a reflection type in which a reflection plate is provided that reflects light impinging upon the front side, and a semi-transmission type which functions as both transmission type and reflection type.
In particular, in business machines and apparatuses for home use, a simple matrix structure reflection type liquid crystal display device is used because the element construction and the driving mechanism are both simple and the cost is low.
FIG. 4 is a partially cutaway perspective view showing an example of the conventional simple matrix structure STN reflection type liquid crystal display device. In this reflection type liquid crystal display device 1, a pair of glass substrates (transparent substrates) 2 and 3 are opposed to each other. A phase difference plate 4 and a polarizing plate 5 are sequentially formed on the upper surface of the glass substrate 2 (which serves as the upper substrate). An insulating layer 6 consisting of SiO2 or the like, a transparent electrode 7, and an orientation layer 8 are sequentially formed on the lower side of the glass substrate 2. A reflection layer 9 consisting of a metal layer, a stripe-shaped color filter 10, a flattening layer 11 making the upper surface of the color filter 10 a flat surface, an insulating layer 12 consisting of SiO2 or the like, a transparent electrode 13 consisting of an ITO layer, a NESA layer or the like, and an orientation layer 14 are sequentially formed on the glass substrate 3 (which serves as the lower substrate). A liquid crystal layer 15 is formed between the orientation layers 8 and 14 to provide a liquid crystal display module 16.
Above this liquid crystal display module 16, front lights 19 are formed at fixed intervals. The front lights 19 include a large number of grooves 18 having a substantially V-shaped sectional configuration that is of a stripe pattern formed on the upper surface of the glass substrate (transparent substrate) 17.
In this reflection type liquid crystal display device 1, as shown in FIG. 5, the angle xcex8 made by the stripe-shaped color filter 10 and the grooves 18 of the front lights 19 is set to be in the range of 0 to 50 degrees.
Further, in an active matrix type liquid crystal display device using a TFT (thin film transistor) which is another example of a reflection type liquid crystal display device, the angle made by the stripe pattern of the color filter and the stripe pattern of the front lights is set to be 22.5 degrees.
Incidentally, in the above-described reflection type liquid crystal display device, the stripe-shaped color filter 10 is inclined by the angle xcex8 with respect to the grooves 18 of the front lights 19, so that when light L is projected onto the liquid crystal layer 15 from the front light 19, a fringe-like diffraction image, that is, a moirxc3xa9 fringe M, is generated, resulting in a deterioration in the color image quality.
In these moirxc3xa9 fringes M, the inter-fringe distance is larger than the width of the groove 18, so that, in particular, when generated in a color image, the color image is greatly deteriorated due to these moirxc3xa9 fringes M, and in some cases, it is completely impossible to obtain a clear color display.
In this way, the moirxc3xa9 fringes M greatly influence the hue, brightness, saturation, etc. of the liquid crystal display module, so that they lead to generation of problems such as a deterioration in clarity in color display, generation of color inconsistency, and unclearness in color separation, resulting in a deterioration in the color image quality.
The present invention has been made in view of the above problem Accordingly, it is an object of the present invention to prevent the generation of moirxc3xa9 fringes to thereby realize an enhancement in color clarity, a reduction in color inconsistency, clearness in color separation, etc., and provide a liquid crystal display device with an improved color image quality of the display screen.
To achieve the above object, in accordance with the present invention, a liquid crystal display device is provided that comprises a liquid crystal display module in which a liquid crystal layer and a color filter are formed between a pair of opposing transparent substrates, and a front light mounted to the front side of the liquid crystal display module. In addition, the stripe pattern of the color filter is substantially perpendicular to the stripe pattern of the front light.
In accordance with the present invention, in the liquid crystal display device the angle made by the stripe pattern of the color filter and the stripe pattern of the front light is in the range of 90xc2x110 degrees.
Further, in accordance with the present invention, in the liquid crystal display device the stripe pattern of the color filter comprises a plurality of stripe-shaped color filters arranged in the short side direction and the stripe pattern of the front light comprises a plurality of grooves formed in the main surface thereof.
In this liquid crystal display device, the stripe pattern of the color filter is substantially perpendicular to the stripe pattern of the front light. Thus, even when light is projected from the front light toward the liquid crystal layer, stripe-like diffraction images (i.e. moirxc3xa9 fringes) will not be generated.
In the liquid crystal display device according to the above embodiment, moirxc3xa9 fringes will not be generated or visually recognized because the angle made by the stripe pattern of the color filter and the stripe pattern of the front light is in the range of 90xc2x110 degrees. If the angle made by the stripe pattern of the color filter and the stripe pattern of the front light is out of this range, moirxc3xa9 fringes will be generated and visually recognized, thereby resulting in a substantial deterioration in the color image quality of the display screen.
In a liquid crystal display device according to an alternative embodiment, moirxc3xa9 fringes will not be generated or visually recognized when an optimum angle exists between the stripe pattern of the color filter and the stripe pattern of the front light. In this case, the optimum angle may be determined by a combination of a width of the color filter, a distance between the color filter and an adjacent color filter, a width of each of the grooves, and a distance between adjacent grooves.
Thus, moirxc3xa9 fringes will not influence the color hue, brightness, saturation, etc. of the liquid crystal display module and no deterioration in the clarity in color display, generation of color inconsistency, unclearness in color separation, etc., will exist. This makes it possible to improve the color image quality of the display screen.